Ball and socket joints are used in a variety of applications, including rack and pinion inner tie rod socket assemblies, steering knuckles, drag links and connecting rod assemblies. Ball and socket joints typically include a generally cylindrical socket member adapted to receive a compressed bearing together with a head of a ball stud. The compressed bearing reduces the friction level between the socket and ball stud head. Over time, the bearing expands to compensate for wear.
Ball and socket joints including bearing halves have known disadvantages. In particular, existing joint bearing halves can adapt for only limited wear, resulting in a loose fit between the bearing and the stud head. Over time, when a joint becomes less tight, stud rotating torque decreases and axial end play increases, decreasing joint performance and resulting in potential joint failure.
The prior art teaches the use of a two-piece bearing set which promotes easier joint assembly and a tighter joint. However, an excessive compression pre-load may be applied such that the bearing plastically deforms. When a bearing plastically deforms there is a lack of balance between elasticity or shock absorption and compressibility or torque control.
Further, the need for materials having low friction characteristics for maximum joint life tends to dictate the use of synthetic non-metallic bearing materials. But the surface of the ball stud is usually machined, leaving microscopic imperfections thereon. Any imperfections in the ball tend to deteriorate the inner bearing surface and reduce the ability of the bearing to lubricate the ball joint. Abrupt or sharp edges on the ball surface also tend to remove lubrication from the bearing surface, increasing joint friction. The inner bearing surface of "dry" bearing halves (bearing halves with no added lubrication) may become damaged and/or scored due to surface irregularities of the ball stud.